Problem: In geometry class, the girl to boy ratio is $6$ to $10$. If there are a total of $80$ students, how many girls are there?
A ratio of $6$ girls to $10$ boys means that a set of $16$ students will have $6$ girls and $10$ boys. A class of $80$ students has $5$ sets of $16$ students. Because we know that there are $6$ girls in each set of $16$ students, the class must have $5$ groups of $6$ girls each. There is a total of $30$ girls in geometry class.